Purification of anthraquinone



alkeli -solutiou-until no furtlies nuricetion a.ntliraquinone,obtainedby tbe chromic acid ff-method of oxidation, are added to 1200ports of cheated caustic sode. solution in e -vuvequipped with anagitator, and 75. erts of zinc dust are added over e period o sev yeralminutes, the contens of the vat being kept at @temperature of-ebou C.,and

egrtuted esilio same time. lit-is important to avoid too hightemperatures, as these tend to bring about` objectionable ,overmeductlomfllie temperature can be regulated by suii able beating or cooling coilsand by the rabe anthraquinone,

f o'l introduction of elle zinc ,dust The re-l `duction operation iscontinued under the saineconditions oftemperet-ure und" ugi'se.u

tionor e uriberperiod of? time of e. g, 15 to minutes. The Zine sludge,together with the alkali insoluble. impurities are. re-

moved by filtriion, fthe filtration being promoted by steam pressurewhich else prote'cis elle solution against objectionable'oxidation.

Any unrcduced enilnuquinone, as well es v'the moher liquor, is removedby washing: 'the press cake in elle ilzer press with warm 35% causicsode solution until the Washings are no longer colored red by thereduced anflbet is, any unreduced en'- ,tlie edded caustic alkali andthe free zinc coumi'ncd in f-he sludge so that it will pass into tbelcrete and in this Way ine-removed from ibesludge.l The alkaline ilte'teend wesh liquor.: contain "the reduced anthrw.

quiiione-iu solution together. with such im 'puriies as ere soluble inthe alkaline' solu ytion.y Tins 'solution vv1s omdizedr by contact jelle with eil, 'by blowing air through it and ;u.ccipitate'd'v entliraqumonev is; removed byv ii-lretion und is treated with a hot dilutealliu-line solution and the Washing with this solution is 'continueduntil there is no fur-- ther. purificationlto be 'ei'eced and finally isYWashedwili Water alone,I Forcertain'types- 6) of crude'untbraquinoneVlie process cen be :modified to include 'an ecid'yyash.

The complete process of purifica-tion of resent inveneion muy beconsidered to inve ve 'liree successive sieges of purifica- ,ln thefirst segc of che puricution, those impurities in tbe crudeeutlirequiuonc, wbelier orno reduccd'by 'the' treatment. with zinc endcaustic soda, which are 'in-k soluble in the alkaline media, are leftbehind .on the lter at che end of the lirst operation;

'while :lie entlixaquinone, Wliicli lies been reduced io e form solublein the alkaline solu- Jtion, es well es euch irnpuriiies es are like?.wies-semble ehe sodium nydrosldeee Losses? tion, go into the filtrate..During the filter7 ing operation, as above noted, the solution andprecipitate are protected from objectionable oxidation and thelteringoperetion .is promoted by the use ofv steam pressure. The insolubleimpurities which are removed in this operation include the excess zinc,hydrocarbons, elkeliinsoluble niirogenous bases, and such oxidationAproducts as are insoluble in alkali, such :is unreducedphenantbrequinone, ecenaptliequinone, and vsome chromium oompounds. Thefiltrate contains tbe. reduced anthraquinone usually vtogeher with someplienantliraquinone, scene htbaquinone, so dium silicate, alkali solub echromium complexes, end phenolic and cerboxylic'compounds .l'n thesecond purification operation, the blowing' of air through theliltrubecontaiu ing the reduced enzliruquinone in the elke linesolution' causes oxidation and preclpiau tion of the'enthraquinonetogether willi-such .impurities as may be present and likewiseprecipitated through sir oxidation, Whereas ibo filtrate Will containsuoli impurities'as remain soluble under these conditions. Theprecipitate may thus contain, in addition to .the antliraquinone, aperi; of the phenenehraquinone, acenepbtliaquinone,and 'zinc salts orlakes of these; While the filtrate contains,

one is treated with hot diluteellzeli with rei i sulting removal olmpuritieswliich ure in-l soluble inl alkali.

During the reduction cold elksill, but soluble in hoi;v

stage of the process,

during which the crude anisliraquinone is subjected. to reduction withthe zinc and caustic solution, i'ftbe mixture-is heated at too biglie,temperature end 'for toolong u period of time, or if the, causticsolution is teostron there Willbe formed some reductionplo ucts ofsutbrequinone which are .'not readily oxidized to untbraquinone by theaction of air; and it is therefore importent to control elle conditionsof the reduction so'tbat che' anhraquinone will be reduced as cemletelyse possible to a solublel forni with su stfxintial avoidance of thesemore dif-- iculty oxdizeble reduccion products.

@n the other' hand, the degree of the reduction voperation shouldbesuilioient to reduce substantially all of the inrithraquinoue'- to liemoreeasily oxidizable reduction prod ucts, and the reduction treatmentshould be .suited to the accomplishment of this result- TeZiiilc-a uutheseine time" avoiding 'the dilicul-` meschers msniicned, The process ofdie i y j v Losses? and' subsequently oxidizing the :separated peratureof about'ZO-LOO 0.,-for u period of y' about 5-60 minutes, separatingthe solution.

solution and treating the precipitated an thruquinone with the dilutealkslii.f y

7. The method of purifying anthraquinone from impurities containingchromium,

which comprises subjecting such impure anthraquinoneto reduction withzinc and c soiution containing about 5% caustic soda at afregulatedtemperature ci about 20 to 40 C., separating the resulting solution fromthe insoluble residue While protecting "the solution froml oxidation`'oxidizing the resulting, solution, and ltering off the an thraquinone'and treatingit With alkali to remove alkali soluble impurities. u

8n tlie method of purifying an impure antbraquinone,-the steps whichcomprise subjecting labout 100 parts by. Weight of i1np111e.untli1aquinone to the reducing action ofibout 1200 purts by Weight ofabout a 5 per cent caustic soda solutionl and about 75 purts by weight of zinc dust at `a telncontaining the reduced anthraquinone from theinsoluble residue, and subjecting the sepfirated solution to the uct-ionof an oxidizing agent to from. i i

' 9. The Inet-bod of reducing anthraquinone which comprises subjectinganthraquinone to tbe action of zinc in the presence of about a five percent solution of caustic alkali ai;v

a temperature of about 20 to 40 C.

10. In the-reduction of anthraquinone by,

means of zinc in the presence of a solution of caustic alkali,suiiiciently dilute to prevent the, formation of considerable amounts ofprecipitate la nthruquinone `tl'ieree v diiicultly oxidizable reductionproducts ofy;

anthraquinone' the step which comprises.-m

causing the reaction to occur at a tempera-,v` y

ture of about 20 to 40 lC.

In testimony whereof I a'ix my signature, HARRY F. LEWIS,`

